2.1 Sampling Techniques
Zooplankton samples were collected in the
late austral summer of 1991 (from February
20 to March 4) by the RN Cariboo
(Guglielmo et al. 1993). Nineteen stations
were sampled from 30 to 1120 m depth along
the main latitudinal axis of the Straits (52°54°S latitude; 69°-73°W longitude) (Fig. 2.1).
Station and sample data are given in Table
2.1.
Samples were taken with an EZNET
BIONESS (Easy Zooplankton Net - Bedford
Institute of Oceanography Net and Environmental Sensing System) (Sameoto et al.
1980). This is an opening and closing net
sampler equipped with ten nets with a mouth
opening of 0.25m 2 . The EZNET BIONESS
was fitted with three types of plankton nets;
one IOOO-Jlm net followed by five 500-Jlm and
four 230-Jlm nets alternately arranged on the
main frame. For the present study, only the
data from the 230-Jlm nets are reported.
The EZNET BIONESS continuously
recorded temperature, salinity and light
attenuance with a KMS II (ME Meerestichnik
Elektronic GmbH) multiparametric probe.
Also, oxygen concentration was measured
with a calibrated oxygen electrode mounted
on the KMS II. Flow velocity through the
nets was monitored with external and internal
acoustic doppler flowmeters (SM 21HME Meerestichnik Elektronic GmbH).
Chlorophyll a concentration was measured
with a Mie-Backscat Fluorometer (Haardt
Optik Mikroelektronik) mounted on the
EZNET BIONESS.
The EZNET BIONESS was towed at a
speed of 1.5-2m/s while it was slowly
lowered along an oblique path to the desired
Chapter 2 Materials and Methods
depths, whereupon the nets were opened and
closed by command from the ship. The
volume of water filtered for each sample
varied from 20 to 300m 3 with greater
volumes filtered at increasing depths due to
the assumption that zooplankton-abundances
would be less at depth.
A series of discrete samples were collected
from the surface to 900 m during both day
and night. The depth layers were chosen
so as to sample the water column above
the thermocline in greater detail. Sampling
stopped approximately 20-40 m from the
bottom and, in many cases, only a few meters
above the bottom. The distance from the
bottom was calculated using a PSA 900 Data
Sonic echosounder mounted on the EZNET
BIONESS.
Samples were preserved in a 4% buffered
formaldehyde-seawater solution. The entire
sample was sorted for macrozooplankters
(> 1 cm in length) which were removed and
identified. The remaining sample was then
processed for the present copepod study.
Copepods were counted and identified to
species level, and distinguished as females,
males or copepodite stage. Population
abundances were estimated as the number of
individuals per 100 m 3 of water filtered.
2.2 Terminology, Measurements and
Line Drawings
The taxonomic descriptions are based on
adult morphology. General body structures
are described according to the terminology of
Huys and Boxshall (1991). The abbreviations
used in the descriptions are listed below:
Zooplankton samples were collected in the
late austral summer of 1991 (from February
20 to March 4) by the RN Cariboo
(Guglielmo et al. 1993). Nineteen stations
were sampled from 30 to 1120 m depth along
the main latitudinal axis of the Straits (52°54°S latitude; 69°-73°W longitude) (Fig. 2.1).
Station and sample data are given in Table
2.1.
Samples were taken with an EZNET
BIONESS (Easy Zooplankton Net - Bedford
Institute of Oceanography Net and Environmental Sensing System) (Sameoto et al.
1980). This is an opening and closing net
sampler equipped with ten nets with a mouth
opening of 0.25m 2 . The EZNET BIONESS
was fitted with three types of plankton nets;
one IOOO-Jlm net followed by five 500-Jlm and
four 230-Jlm nets alternately arranged on the
main frame. For the present study, only the
data from the 230-Jlm nets are reported.
The EZNET BIONESS continuously
recorded temperature, salinity and light
attenuance with a KMS II (ME Meerestichnik
Elektronic GmbH) multiparametric probe.
Also, oxygen concentration was measured
with a calibrated oxygen electrode mounted
on the KMS II. Flow velocity through the
nets was monitored with external and internal
acoustic doppler flowmeters (SM 21HME Meerestichnik Elektronic GmbH).
Chlorophyll a concentration was measured
with a Mie-Backscat Fluorometer (Haardt
Optik Mikroelektronik) mounted on the
EZNET BIONESS.
The EZNET BIONESS was towed at a
speed of 1.5-2m/s while it was slowly
lowered along an oblique path to the desired
Chapter 2 Materials and Methods
depths, whereupon the nets were opened and
closed by command from the ship. The
volume of water filtered for each sample
varied from 20 to 300m 3 with greater
volumes filtered at increasing depths due to
the assumption that zooplankton-abundances
would be less at depth.
A series of discrete samples were collected
from the surface to 900 m during both day
and night. The depth layers were chosen
so as to sample the water column above
the thermocline in greater detail. Sampling
stopped approximately 20-40 m from the
bottom and, in many cases, only a few meters
above the bottom. The distance from the
bottom was calculated using a PSA 900 Data
Sonic echosounder mounted on the EZNET
BIONESS.
Samples were preserved in a 4% buffered
formaldehyde-seawater solution. The entire
sample was sorted for macrozooplankters
(> 1 cm in length) which were removed and
identified. The remaining sample was then
processed for the present copepod study.
Copepods were counted and identified to
species level, and distinguished as females,
males or copepodite stage. Population
abundances were estimated as the number of
individuals per 100 m 3 of water filtered.
2.2 Terminology, Measurements and
Line Drawings
The taxonomic descriptions are based on
adult morphology. General body structures
are described according to the terminology of
Huys and Boxshall (1991). The abbreviations
used in the descriptions are listed below: